332 University of California Puhlications in Zoology. [Vol. 8 



TABLE 43 

 Surface Distribution of S. hipunctata during Night (6 p.m. to 6 a.m.) 



TABLE 44 



Surface Distribution of S. bipunctata during the time of Maximum 

 Abundance (6 to 10 p.m.) 



In table 43 all four hauls in water having a temperature 

 between 15?9 and 17?5 were made betwen 6 and 10 p.m., while 

 practically half the hauls in water having higher temperatures 

 were made during this period. This means that the 1241 speci- 

 mens obtained per hour when the temperature was 15?9-17?5 

 are not strictly comparable with the numbers obtained from 

 water having higher temperatures. While the table shows that 

 abundance and frequency decreases as the temperature increases, 

 the amount of decrease is less than that found during the twelve 

 hours of daylight (table 41). Finally table 44 shows that the 

 amount of decrease is still less during the time when the species 

 migrates in maximum numbers to the surface. In fact, the 

 table shows an actual reversal in abundance and frequency rela- 

 tive to temperatures between 17?6-19?5 and 19?6-21?5. This 

 reversal is probably due to the small number of hauls, but it is 

 significant that the effect of high temperature on abundance 

 and frequency of this species is less during twilight than during 

 any other period of the day. 



It was noted on page 121 that the number of specimens on 

 the surface decreases abruptly after evening twilight vanishes. 

 The above relations discovered between temperature and dis- 



